Aperture mask for color tv picture tubes and method for making same

ABSTRACT

APERTURE MASKS FOR COLOR TV PICTURE TUBES ARE FORMED INITIALLY WITH THE HOLE PARTIALLY CLOSED FOR USE IN LAYING DOWN PHOSPHOR DOT PATTERNS ON THE TUBE SCREEN AFTER WHICH THE HOLES ARE OPENED FOR NORMAL OPERATION OF THE MASKS AS PART OF THE FINISHED TUBE.

April 6, 1971 J. J. FRANTZEN APERTURE MASK FOR COLOR TV PICTURE TUBES AND METHOD FOR MAKING SAME Flled Jan 6 1969 INVENTOR L/d/IN d. RANT'ZEN BY A ORNEYS United States Patent O U.S. Cl. 156-8 7 Claims ABSTRACT OF THE DISCLOSURE Aperture masks for color TV picture tubes are formed initially with the hole partially closed for use in laying down phosphor dot patterns on the tube screen after which the holes are opened for normal operation of the mask as part of the finished tube.

BACKGROUND OF THE INVENTION This invention is involved generally with the fabrication and assembly of color TV picture tubes containing aperture masks and, in particular, is concerned with the manufacturing steps in which the aperture mask is first used to form the phosphor dot pattern on the face plate after which it is permanently attached inside the tube for normal operation.

Conventionally, the three primary color phosphor dots are formed on the inside surface of the glass face plate of a color TV picture tube using an aperture mask and after these dots have been formed the same mask is permanent- 1y attached in the tube to provide its normal function of directing the electron beams to strike the proper phosphor dots. In this invention, the permanently attached aperture mask contains openings which are somewhat larger than those in the same mask when it was used for forming the phosphor dots.

Conventional color TV aperture-mask picture tubes, various processes for forming the three primary color phosphor dots on the viewing face of the tube and the construction, operation and function of the aperture mask are all disclosed and described in the prior art, for example, in an article titled Constructing the Tri-Color Picture Tube, Electronics, p. 86 published May 1951; in US. Patent 3,146,368 to Fiore et a1. dated August 1964; in US. Patents 2,795,719 to Morrell and 2,802,964 to Iesty dated August 1957. conventionally, the primary color phosphor dots are formed using techniques which involve using the same aperture mask that is eventually made a permanent part of the picture tube. This is because the relative locations of the dots and the mask apertures are so critical that it has been extremely difiicult to use one mask for dot forming and to substitute another mask for it for focusing purposes and yet obtain exact reproducibility, even though both masks might have been made from the same basic pattern. However, there is a big disadvantage in using the same mask for both functions. The mask must have smaller-sized holes or openings when used to form the phosphor dots than are necessary for focusing, but these smaller openings reduce the brilliance of the picture during normal operation from what might otherwise be with somewhat larger openings.

To overcome this disadvantage, a number of schemes have been devised. One of these is described in the Law US. Patent 3,231,380. In this idea, the aperture mask is formed in the conventional manner using photographic techniques to form a pattern in a protective coating of enamel over a sheet of metal and then etching out the holes to the largest usable size. Then, while the enamel is still in place, the holes are partially filled with a material different from the base metal. This mask is then used for forming the phosphor dot pattern but before the mask is 3,574,013 Patented Apr. 6, I971 permanently installed in the tube the filling material is removed from the openings to return them to their original dimensions. While this scheme works in theory, there are practical limitations. For one, once the coated metal has gone through an etching bath or spray, the enamel that remains has usually deteriorated sufficiently that it can no longer serve as an adequate protective coating. For another, before the mask can be used to form the phosphor dot pattern, it must be shaped aspherically or domed which requires mechanical working and heat treating which would destroy the enamel coating. To fill the openings before the mask is domed is impractical because the shaping would alter the size and shape of the openings.

SUMMARY In this invention the base metal aperture mask is formed in the conventional manner, using photoprinting and chemical etching techniques, and is then shaped or domed with the enamel coating removed. For forming the phosphor dots, the openings in the mask are partially closed. After the phosphor dots have been formed on the face plate, the openings are enlarged back to their original size. According to the teachings of this invention the mask is at least made double layered, one of the layers having smaller apertures. After the phosphor dots have been formed the smaller-opening layer is removed while the largeropening layer remains. In one embodiment, two separate aperture mask are made from the same matrix plate and formed on the same die but with one of these masks having somewhat smaller openings than the other. The tWo masks are brought together in register for forming the phosphor dots but afterwards the mask with the smaller openings i removed and the larger-opening mask is installed permanently in the picture tube. In another embodiment, the base metal mask is coated with a material to partially close the openings after the mask has been domed and the coating material is stripped away after the phosphor dots are formed.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat functional partial cross-section view of the forward part of a color TV picture tube, great- 1y simplified, illustrating the arangement of the component parts with which the present invention is involved;

FIG. 2 is a somewhat enlarged, simplified, cross-sectional view of a portion of FIG. 1 illustrating an embodiment of the invention of a mask with a covering layer on one side partially closing the openings; and

FIG. 3 is a view similar to FIG. 2 illustrating another embodiment of this invention having two separate masks in register.

DESCRIPTION OF THE PREFERRED EMBODIMENT The conventional color TV aperture mask picture tube has a glass face plate or viewing face 10 which is coated on its inside surface with a layer of phosphor dots 11 representing the three primary colors. In the drawing the phosphor dots are represented as a uniform layer 11, there being no intent to illustrate the dot pattern. Within the tube envelope and located between the electron guns, not shown, and the phosphor layer 11 is an aperture mask 12 ordinarily made out of a thin sheet of metal, such as stainless steel, for example, and containing a translucent area formed by a myriad of miniature openings or apertures through which the electron beams pass when traveling toward the face plate 10 to strike the layer of phosphor 11. The electron guns which eject the electron beams are located at the rear of the picture tube within the funnel shaped glass closure 15. Other component parts of the picture tube such as shields, deflecting plates or coils, mounting hardware for the aperture mask, etc. have been deleted to simplify the drawing since they do not constitute an essential part of the invention nor are they necessary to fully describe the present invention.

Processes used to form the phosphor layer 11 on the face plate are well known in the art and are described in detail in publications such as Kaplan U.S. Patent 2,959,483. As set forth in greater detail in the prior art, briefly this process may involve initially coating the inside surface of the face plate 10 with a first primary color phosphor in a sensitized carrier and exposing this coating to a suitable source of energy, such as light, through an aperture mask 12. Where the light strikes, hardened spots of the first color phosphor are formed and the unhardened areas are then washed away and removed. This is followed by applying a layer of a second primary color phosphor in a suitably sensitized carrier and exposing the second layer to an energy source through the aperture mask 12 in the same manner as before. Either the beam from the energy source or the mask is shifted slightly so that the newly exposed areas are slightly displaced from those exposed earlier. The unhardened areas of the second layer of phosphor are then washed away and removed. Finally, the third primary color phosphor coating is applied and processed in a similar manner with the dots formed thereby being slightly displaced from the other two sets of phosphor dots. By this process there are formed sets of elemental areas comprising a triad of three discrete primary color phosphor dots. It is quite critical that each of these discrete dots be precisely located with respect to one another within a triad and that each triad be precisely located with respect to the other triads. Because of minute, almost imperceptible differences that may exist between aperture masks, it is best and virtually mandatory, with the present state of the art, that the same mask be used to form each of the three colored dots and that this same mask be permanently assembled in the picture tube for its operational function of guiding the electron beams onto the respective phosphor dots.

Turning first to FIG. 2, the base mask 12 can be made using well-known photoprinting and chemical milling or etching techniques and process steps which are described in the prior art such as in the Electronics article, supra, or in Mears US. Patents 2,762,149 and 2,822,635 and other patents referenced therein and in what is now regarded as a conventional manner, but with some variations. As described in greater detail in the prior art, briefly these process steps include coating a thin sheet of metal, such as .01 inch stainless steel, with a sensitized enamel or the like and then exposing the sensitized coating to a suitable light source through a plate containing an array of opaque and transparent areas including miniature dot-like areas defining the desired aperture pattern. The plate is ordinarily a positive so that light will not strike those areas which are to form the openings in the metal sheet so that the sensitized coating will not harden in those areas and will be washed away after exposure by subsequent developing treatment. In the ordinary procedure, the dot pattern is photoprinted similarly in register on both sides of the metal, with the dots on one side being somewhat smaller than their counterparts on the other side. But here the smaller dots are photoprinted on the other side using a negative plate which means that after exposure and developing the enamel coating will remain only in the dot areas and will be removed from all other areas.

After the desired patterns have been photoprinted and developed out as described, layer 12a is plated on the side of mask layer 12 which contains the small enamel dot areas. This can be done, for example, by using well-known electroforming techniques in which the metal layer 12 with the enamel is immersed in a suitable bath so that the side to be plated is facing an anode of suitable material and the other side being protected in some convenient fashion so it does not become plated over. Although a number of different plating materials can be used, one of the preferred metals is zine because it has the necessary characteristics which enable it to withstand the subsequent processing operations that the plated metal must go through. For reasons which will become apparent later, an essential characteristic of the plating metal is that it must not react with nor be attacked by the same chemical etchant which is used to etch out the holes in the base metal. The thickness of the plating layer should be monitored because this thickness will affect the effective size of the mask opening. In those areas where the openings are to be closed up the most, the plating may be heavier or thicker. Naturally the dimensions of the enamel dots on this side of the base metal must be chosen so that they will be optimum size for the operation of forming the phosphor dots.

After plating, the base metal layer 12 is then sprayed with a chemical etchant applied to its other side. This is done in the conventional manner using, for example, ferric chloride having a suitable Baum, if the metal is steel, which is preferred. The spray is applied and controlled until the apertures or openings 13 have been milled out to the desired dimensions. It should be noted that the shapes of openings :13 illustrated in the figures are ideal. As a practical matter, however, the openings are made with a somewhat tapered effect so that they are larger on the unplated side of the metal base 12 than on the plated side. The etchant used on the base metal does not attack nor react with the layer 12a but it does remove all of the underlying support for the small dots of enamel which define the small openings 14 on the plated side so that the openings now pass completely through both layers 12 and 12a. Typically, the smallest dimension of apertures 13 is in the order of .016 inch diameter and the smallest dimension of openings 14 is in the order of .008 inch at the central area of the mask and may increase in a graded manner up to approximately .009 inch near the outer edges of the mask. Without getting into details, the graded hole sizes are necessary for properly forming the phosphor dots. After the openings have been made through the two layers, all the remaining traces of enamel are then removed in the conventional manner by applying a suitable hot caustic solution followed by cleaning and drying.

Next, the mask 12 with its plating layer 12a is domed and otherwise processed in the conventional manner which involves annealing and roller-leveling as well as other process steps. These are steps 'With which those engaged in the field of making TV aperture masks are familiar and they do not constitute part of the present invention so are not set forth in any detail here. Suffice is to say that, as explained earlier, the plating material for layer 12a is chosen so that its characteristics will enable it to withstand the temperatures and the forces applied during these operations without changing substantially. The double-layered mask is now in a form such that it can be used in the phosphor dot process. As stated earlier, this process is not a part of the present invention and the process steps are well-known in the art and are set forth in detail in a number of publications, supra. Suffice it to say that it is the smaller openings 14 which control in the phosphor dot process. Once the phosphor dot layer 11 has been formed on the face plate 10, the plating layer 12a is no longer needed and, as a matter of fact, if allowed to remain would reduce the brilliancy of the picture produced on the viewing face of the tube. Therefore, this layer is then stripped away. Preferably, this is done by using a suitable chemical etchant which will attack the material of layer 12a but will not have any substantial effect on the material of mask layer 12. The particular steps which are used to remove the plating layer 12a are not critical and a suitable etchant having the necessary constituency and characteristics is a matter of choice and can ordinarily be selected by one of ordinary skill in the art. Of course, it goes almost without saying that the plating layer 12a must be removed without physically affecting the mask 12 so that it will retain its initial size, shape, hole locations, etc. With the layer 12a removed, the mask 12 is now ready for permanent installation in the picture tube to serve its normal function with the result that the picture produced at the viewing face of the tube will be in the order of more brilliant than is the case with smaller openings in the aperture mask.

Turning next to FIG. 3, aperture mask 12 can be combined initially with a separate mask 12b made in a number of ways. The mask 12 containing the larger-sized apertures can be formed using the conventional photographic and chemical milling techniques which are so thoroughly known in the prior art. The other mask 12b can be formed in an identical fashion but with smaller appertures 14 which would be the same size as the openings 14 in the embodiment shown in FIG. 2. These both must be made from the same master plate and control of the etching should be used to reduce the size of the apertures in the second mask. This is for the reason that the two must eventually be arranged in overlaying fashion, as shown in FIG. 3, with their respective openings in exact register with one another. Another way of making the two masks is to first make mask 12 with larger openings using well-known electroplating or electroforming techniques. This involves electroplating on a die or matrix plate or other carrier member, a layer of metal containing the desired pattern of larger-sized apertures. This layer is then stripped off the carrier plate and another layer of metal is electroformed on the same carrier plate but this time the process is continued on for a slightly longer period of time so that the layer of metal is thicker and the openings are somewhat smaller than before. Since both masks would then have been made on the same die, their respective openings would have to fall exactly on center with one another. Regardless of which way the two masks are made, it is equally important that they both be domed or formed in the same die and under identical conditions so that they will fall in exact register when used together in the phosphor dot forming operation. Actually, once it is established that the two masks are in register, then only mask 121;, with the smaller openings, need be used to form the phosphor dots after which it can be replaced with mask 12. Since the only reason this embodiment requires two masks is to confirm that the smaller-opening mask is in exact registration, it can be seen that once this has been established a single smaller-opening mask can be used over and over again with a number of separate larger-opening masks 12.

As a variation of the embodiment of the invention described and illustrated in FIG. 2, it is possible that the mask layer 12 initially can be made in the conventional manner using the well-known photographic and chemical milling techniques. This involves etching out apertures 13 from both sides of the base metal after both sides of the metal have been photoprinted with positive plates in exact register. After apertures 13 have been etched out, all the remaining enamel is then removed in the conventional manner. Afterwards, layer 12a is plated on the one side of base metal 12, such as by electroplating, and a layer of the same material may be plated on the other side without using enamel or the like to define the areas to be plated over. What results is that some of the plating material may be deposited along the walls of the apertures 13 to partially close them up and the size of the openings may be more accurately controlled. To repeat, typically these openings range from about .008 inch diameter in the central area of the mask to approximately .009 inch diameter at the outer edges and this involves a multitude of tens of thousands of holes. After the triple-layered mask made in this manner has been used to produce the phosphor dot pattern, the outer layers are then stripped away in some convenient fashion, e.g., chemical etching such as described briefly above. In both cases, i.e., plating metal on one or both sides to partially c ose up the holes, the plating preferably should be done while the mask is still fiat although it can be done after doming, etc., provided proper control of the plating process is maintained.

I claim:

1. For use with a color television picture tube, a mask for laying down a pattern of colored phosphor dots on the face plate of the tube and for later functioning as an aperture mask during normal operation of the tube, said mask comprising in combination:

(a) a metallic sheet containing a multitude of tiny holes laid out in a predetermined pattern, the said holes being of a predetermined size for optimum operation as an aperture mask in a picture tube;

(b) a layer of opaque material made out of metal containing a multitude of tiny holes laid out in the same predetermined pattern as in said metallic sheet, the said holes being smaller than those in said metallic sheet;

(c) said opaque material layer being arranged coextensive and in register with said metallic sheet such that the respectively corresponding holes are centered to one another; and

((1) said sheet and said layer being bonded together rigidly in a manner such that said opaque layer may be separated from the metal sheet without harming said metallic sheet.

2. The invention as in claim 1 wherein said opaque layer is made out of metal dissimilar to said metallic sheet and is bonded to said metallic sheet by electroplating.

3. A method for making a mask useful for laying out color phosphor dot patterns and for functioning as an aperture mask in a completed color television picture tube, said method comprising the steps of:

(a) making a fiat metal mask containing a multitude of tiny apertures arranged in a pattern and having dimensions suitable for optimum operation as an apgrture mask in a completed color television picture tu e;

(b) forming said mask to a shape suitable for use in a color picture tube;

(c) making and forming another mask containing a multitude of tiny apertures in identical pattern and locations as in said first-mentioned mask with said apertures being dimensioned smaller than those in said first-mentioned mask and placing said first and said another mask in coextensive overlaying relationship so that the respectively corresponding apertures in each are in register with one another; and

(d) separating the second mask from the first mask without damaging said first mask after the combined mask has been used to lay out the phosphor dots.

4. The method as described in claim 3 wherein said another mask is made and placed on said first mask by the steps of:

(a) defining a pattern of smaller-sized aperture areas on one side only of said first mask in register with the pattern of apertures in said first mask; and

(b) then electroplating a layer of metal on all areas of said one side of the first mask except the aperturedefining areas.

5. The method as described in claim 4 wherein the layer of metal is electroplated on the one side of the first mask when said first mask is fiat.

6. The method as described in claim 4 wherein the layer of metal is electroplated on said first mask after said first mask has been formed.

7. A method for making a mask useful for laying out phosphor dots and for normal operation as an aperture mask in a color television picture tube, said method comprising the steps of:

(a) coating one side of a thin sheet of metal with a protective coating except on those areas which define aperture areas and the other side with a protective coating only on the aperture-defining areas, said aperture-defining areas on each side being in exact register with one another and being smaller on said other side;

(b) electroplating a layer of metal which is dissimilar from said first-mentioned metal, on the uncoated areas of said other side of said metal sheet to at least partially close up the aperture defining areas;

(c) etching away the uncoated areas from said one side of said metal sheet without affecting the metal layer on said other side;

((1) forming the etched metal sheet with the electroplated layer to the desired shape for use in the picture tube; and

(c) after using the double-layered mask for laying out phosphor dots, etching away the electroplated layer without disturbing the first metal sheet.

I. T. GOOLKASIAN,

References Cited UNITED STATES PATENTS Primary Examiner 10 J. C. GIL, Assistant Examiner U.S. Cl. X.R. 

